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Photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices. Team: Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien.

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Présentation au sujet: "Photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices. Team: Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien."— Transcription de la présentation:

1 Photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices. Team: Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien Daquin, Michel Broquier. Raphaël THON Doctorant deuxième année Journées de lEDOM 7 et 8 Mars

2 Atmospheric interest Astrophysic interest Sugar model C n H 2n O n Fundamental studies. (Hydrogen bond) Frozen molecules in the ground states (simplified spectra) High quantities Environment effects Glycolaldehyde in cryogenic cristalline matrix. Why? 2 C2H4O2C2H4O2

3 Photochemistry: ultraviolet irradiation Infrared diagnostic Glycoladehyde in Argon matrix (T=10K) UV irradiation by excimer laser emitting at 193nm or 248 nm. 3 Gas phase: Different dissociation pathways Isomerisation HOCH 2 CHO ( Cc ) HOCH 2 CHO ( Tt ) + h ν HOCH 2 CHO (Cc) + h ν CO + CH 3 OH Matrix: products of irradiation Fragmentation

4 Photochemistry: kinetics λ=193 nm All fragments appears at the same time Correlation between Cc disappearance and Tt formation (5) Open geometry only present in matrix Results differ from gas phase. Toward the comprehension of mechanisms 4

5 Vibrational dynamics probed by photon echo Motivations: Influence of environment on vibrational modes Coupling between vibrational modes Method: photon echo produced by degenerate four wave mixing Non linear spectroscopy to separate the two contributions. Homogeneous broadening: hom Inhomogeneous broadening: inhom Dephasing time Population relaxation time Pure dephasing time 5

6 T focalisation sample Detection k2k2 k1k1 t t=-T-τ k3k3 k s = - k 1 + k 2 k3k3 t=0 t=-T ksks k1k1 k2k2 k3k3 Photon Echo: principle Detected signal And: Scanning of τ: measure of T 2, the coherence time Scanning of T: measure of T 1, the population relaxation time 6

7 Experimental set-up 7 Collaboration: Bernard Bourguignon, Aimeric Ouvrard

8 Experimental steps 8 CCl 4 Temporal superposition. Detection of interferences when pulses overlap. FWHM=300 fs Very high dipolar moment: 1D Test on a tungsten hexacarbonyl W(CO) 6 CO streching mode. ν = 1980 cm -1

9 Preminilary results on W(CO) 6 T 2 =2 ps T 1 =620 ps (in liquid ) What about glycolaldehyde in matrix? 9 … to be followed CCl 4 Tokmakoff and al. J.Chem Phys. 100 (12) 15 June 1994 Dephasing timePopulation relaxation time T 2 =10 ps T 2 (matrix) > T 2 (solution) (in N 2 matrix. T=22K) Dephasing time

10 Thank you for your attention. Merci pour votre attention. 10 Acknowledgments Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien Daquin, Michel Broquier, Bernard Bourguignon, Aimeric Ouvrard, Julien Vincent

11 First results on the test solution Measure of the coherence time T 2 =2,57 ps Fit by the following functfion: (exponential decay convolved by the pulse shape) 11

12 Photochemistry: products of irradiation 12

13 Daprès la Thèse dArnaud Cuisset, Dynamique vibrationnelle sondée par écho de photons de DCl et ses complexes piégés en matrices cryogéniques – Thèse Université Paris XI (2003) Photon echo signal

14 10 exp(- /T 2 -i ) exp(-t/T 2 +i t) 3 ème : diffraction : état de cohérence exp(-T/T g ) |1> |0> exp(-T/T 1 ) 2 nde : interférences réseau de populations 11 exp(- /T 2 -i ) exp(-t/T g ) 00 exp(- /T 2 -i ) exp(-t/T 1 ) |1> |0> 1 ère impulsion : Etat de cohérence 00 = 0><0 01 exp(-t/T 2 -i t) |1> |0> Rephasage à t=τ => ECHO de photons k s = - k 1 + k 2 k3k3 e -4 / T2T2 S( ) 0 Photon echo equations


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